This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This trial will evaluate the effectiveness of partial breast irradiation (PBI) compared to whole breast irradiation (WBI) in providing equivalent local tumor control in the breast following lumpectomy for early stage breast cancer. The study will compare the overall survival, recurrence-free survival, and distant disease-free survival between women receiving PBI and WBI. It will also look at quality of life (QOL) issues related to cosmesis, fatigue, treatment-related symptoms, and perceived convenience of care.